Embryology important notes, Study Guides, Projects, Research of Medical Sciences

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Embryology

Embryology

Epiblast

2nd week

Primordial germ cells ( PGC )

Migrate to

Wall of yolk sac

5th week ( PGC again migrate )

Genital ridge ( Testies/ ovary )

PGC Gametogonium Spermatogenesis

Oogenesis

Spermatogenesis

Spermatogonium

Mitotic division

Primary spermatocyte ( 2n )

Meiosis I

Secondary spermatocyte

Sertoli cells (^) Meiosis II

Spermatid

Spermiogenesis

Tight junction (Zona occludens)

Blood testies barrier

Spermatozoa

Spermiation

Release of spermatozoa in the lumen of seminiferous tubule

Epididymis Storage Maturation Motility

Final stage of maturation is also known as capacitation which takes place in female genital tract ( Isthmus of Fallopian tube )

Site for spermatogenesis = Seminiferous tubule

Time take = 72-74 days

1 spermatogonium = 64-512 spermatids

Oogenesis

Oogonium

Before birth

Primary oocyst (2n)

Meiosis I

Arrested in Prophase I ( Diplotene )

Childhood

Puberty

Ovaries are inactive

LH surge (~36 days prior to ovulation )

Meiosis I completes

Secondary oocyte + 1st polar body (n)

Meiosis II

Arrested in metaphase II

Meiosis II is complete only if fertilisation takes place

3rd week

Head end of embryo

Prochordal plate

Week of gastrulation

Tail end of embryo

Epiblast

Hypoblast

Notochord is the first structure defining craniocaudal axis of the embryo

Primitive knot ( Hensen’s node ) Primitive streak

Head Tail

Will give rose to all 3 germ layers

1. Endoderm
2. Mesoderm
3. Ectoderm Head

Prochordal plate ( future buccopharyngeal membrane )

Notochord Ectoderm + endoderm Proliferative mesoderm Primitive Knot

Primitive Ectoderm + Endoderm Streak Cloacal membrane

Tail

Neural crest cells

Neural fold

Neural groove Ectoderm

Mesoderm

Notochord Endoderm

1. Notochord stimulates surface ectoderm to convert it into neuroectoderm
2. Fate of notochord. 1. Nucleus pulposus
   2. Apical ligament of dense
   3. Membrana tectoria ( cranial continuation of posterior longitudinal ligament )
3. Fusion of neural tube begins at cervical region
4. Cranial Neuropore closes on D
5. Caudal neuropore closes on D

Neural crest cells

Neural Somatopleuric lateral plate mesoderm Tube Intra embryonic coelom

Splanchnopleuric lateral plate mesoderm

Para-axial mesoderm Somites

Notochord

Intermediate mesoderm Urogenital system

Lateral plate mesoderm Somatopleuric lateral plate mesoderm

Splanchnopleuric lateral plate mesoderm

Somites

Neural tube

Para-axial mesoderm

D20-D30 = Somite period

Primitive somites = 42-44 pairs

Somites

Occipital somites — 4 Cervical somites — 8 Thoracic somites — 12 Lumbar somites — 5 Sacral somites — 5 Coccygeal somites — 8-

Definative somites = 36-38 pairs

Somite

Dermatome

Dermis of back

Sclerotome (^) Myotome ( Skeletal muscle )

Axial skeleton, Ribs, vertebrae & Annulus fibrosus ( intervertebral disc )

Epiaxial myotome

— Erector spinal — Multifidus

Hypoaxial myotome

— Limb muscle — Abdominal muscle — intercostal muscle

Lateral plate mesoderm

Somatopleuric lateral plate mesoderm

Splanchnopleuric lateral plate mesoderm

Ectoderm

Endoderm

Peritoneal cavity

Intra embryonic coelom (^) Pleural cavity

Pericardial cavity

Somatopleuric lateral plate mesoderm

1. All parietal layers
2. Dermis of ventral body wall & limbs
3. Appendicular skeleton

Splanchnopleuric lateral plate mesoderm

1. All visceral layer
2. Smooth muscle
3. Cardiac muscle ( at the cranial end )

Exceptions in smooth muscle development

1. Sphincter & dilator pupillae — Neuroectoderm

2. Ciliaris muscle — Neural crest cells

3. Smooth muscles of aorta, Pulmonary trunk, Coronary vessels — Neural crest cells

4. Smooth muscles of sweat gland, mammary gland, myoepithelial cells — Surface ectoderm

Derivatives of septum transversum

Buccopharyngeal membrane

Septum Transversum

Undifferentiated lateral plate mesoderm at the cranial end Most cranial structure before folding

1. Central tendon
2. Fibrous pericardium
3. Liver stroma including kupffer cells
4. Ventral mesogastrium — Lesser omantum

Arches Nerves

I Mandibular & chorda tympani

Muscles

Muscles of mastication, TVP, TT, Mylohyoid, Anterior belly of digastric

Arteries

Maxillary artery

II Facial nerve

III Glossopharyngeal nerve

IV Superior laryngeal nerve

VI Recurrent laryngeal nerve

Facial muscles, stapedius, posterior belly of digastric, stylohyoid, Auricular muscle & occipitalis

Stylopharyngeus

Cricothyroid + muscles of palate (except TVP) + muscles of pharynx (except Stylopharyngeus & Cricopharyngeus )

Cricopharyngeus, muscles of larynx (except Cricothyroid)

Stapedial & Hyoid artery

Common carotid & internal carotid artery

Arch of aorta + Right subclavian artery

Pulmonary artery + ductus arteriosus

Development of face

1. Mandibular process ( 1st. Arch )
2. Frontonasal process ( from mesenchyme infront of forebrain )

Frontonasal process

Nasal pits Medial nasal process Lateral nasal process

Maxillary process

Mandibular process

Lower lip — derived from Mandibular process only Upper lip — derived from maxillary process + medial nasal process

Philtrum

Non fusion of medial nasal process —midline cleft upper lip Non fusion of maxillary process & medial nasal process — unilateral cleft upper lip Oblique facial cleft ( nasolacrimal duct is exposed ) — Non fusion of maxillary process to lateral nasal process

Ala — Lateral nasal palate

Palate — medial nasal process & maxillary process

Incisive part

Derivatives of medial nasal process — Tip of nose Anterior part of nasal septum Columella Philtrum Incisive part of palate

Tongue development

Tuberculum impart Lingual swelling

I

II (^) Hypobranchial eminence

III Copula

IV Epiglottis

VI

Tongue muscles are derived from occipital somites (GSE ) except Palatoglossus ( IV arch )

Lining epithelial of anterior 2/3rd of tongue = ectoderm

Limb epithelial of posterior 1/3rd of tongue = endoderm

Cardiovascular development

Somatopleuric lateral plate mesoderm

Septum Transversum

Fibrous pericardium

Cardiac jelly

Myoepicardial mantle

Splancnopleuric lateral plate mesoderm

Parietal layer of serous pericardium

Edndocardial cushions

Cardiac muscles Epicardium ( visceral layer of serous pericardium

Trunkus arteriosus (^) Ascending aorta & pulmonary trunk

Bulbos cordis (^) Conus Smooth out flowing part of both ventricles ( Infundibulum )

Proximal 1/3 rd

Primitive ventricle

Primitive atrium

Rough inflowing part of left ventricle

Rough inflowing part of left ventricle

Rough anterior wall of atrium

Sinus venous Smooth posterior wall of atrium

RH

LH

nte (^) n l ca (^) ot (^) d te y

Development of IVC

Mesonephric vein Mesonephric vein

Right & left supracardinal vein

Intersubcardinal Anastomosis

Right & left subcardinal veins Right & left subcardinal veins

Right posterior cardinal vein (^) Left posterior cardinal vein Right posterior cardinal vein (^) Left posterior cardinal vein Right posterior cardinal vein (^) Left posterior cardinal vein

6

5 Right renal vein = Right mesonephric vein

Left renal vein = Left mesonephric vein + left subcardinal vein + intersubcardinal anastomosis

4 Suprarenal vein = Cranial part of subcardinal vein 3 Gonadal vein = Caudal part of subcardinal vein

(^3 )

2 1 1

Inferior vena cava

1. Right posterior cardinal vein

2. Right supracardinal vein

3. Anastomosis

4. Right subcardinal vein

5. Anastomosis

6. Right hepatocardiac channel

Left inferior vena cava — Drains in left renal vein

Persistence of

1. Left Posterior cardinal vein

2. Left Supracardinal vein

3. Left Subcardinal vein ( till renal segment )

Left gonadal vein drains into left renal vein of left IVC persists

Arter i al system development

Arch of aorta

1. Aortic sac
2. Left horn of aortic sac
3. Left 4th arch artery
4. Left dorsal aorta External carotid artery

Common carotid artery = Proximal part of 3rd arch artery

Internal carotid artery = Distal part of 3rd arch artery + cranial part of dorsal aorta

External carotid artery = Bud from 3rd arch artery

2

Right 7th cervical intersegmental artery 3

1

Lung bud

Left 7th cervical intersegmental artery

Left subclavian artery

Lung bud

Aortic sac Brachiocephalic artery is derived from Right horn of Aortic sac Trunkus arteriosus

Right subclavian artery

1. Right 4th arch of aorta
2. Right dorsal aorta
3. Right 7th cervical intersegmental artery

Pulmonary artery = Proximal part of 6th arch artery

Ductus arteriosus = Distal part of left 6th arch artery

Due to persistence of distal part of left 6th arch artery makes left recurrent laryngeal nerve longer

Right 7th cervical intersegmental artery

Abnormal right subclavian artery

Persistence of caudal part of Right dorsal aorta ( if left 4th arch artery is obliterated ) Caudal part of left descending aorta

Descending aorta

Obliteration of oesophagus Fused dorsal aortae

Dysphasia, lusoria

Interatri al septum

Septum secondum Gives rise to limbus or margin of fossa ovalis

RA LA Foramen ovale

Septum primum Gives rise to floor of fossa ovalis

Endocardial cushion

Atrial septal defect

Usually due to non fusion of septum primum to endocardial cushion

Interventricular septum

1. Endocardial cushion — Membranous part
2. Cardiac muscle — Muscular part
3. Neural crest cells — bulbar septum

Trunkus arteriosus Aorticopulmonary septum ( spiral septum )

Endocardial cushion

Bulbar septum Neural crest cells

Membranous part

Muscular part

Forgut

R espira tor y bud

H epa t i c bud

Ven t ra l pan cr ea t i c bud Dor sa l pan cr ea t i c bud

Septum t ran sv er sum ( m esode rm ) St r oma of the l iv er + Kupffe r cells

Liver

H epa t i c bud ( en dode rm ) H epa tocytes + bi l iary a ppara tus

Pancreas

Dor sa l pan cr ea t i c duct

Ven t ra l pan cr ea t i c duct

Do r sa l pan cr ea t i c bud

Ven t ra l pan cr ea t i c bud

Axia l rot a t i on due to di ffer en t ia l g rowth

Dor sa l pan cr ea t i c bud G iv es ri se to

1. Uppe r hea d
2. Neck
3. Body
4. Tai l

Ven t ra l pan cr ea t i c bud G iv es ri se to

1. L ower hea d
2. U n cina te pr ocess

M ain pan cr ea t i c duct ( Duct of w irsu n g) = v en t ra l pan cr ea t i c duct + di st a l par t of dor sa l pan crea t i c duct

A ccesso r y pan cr ea t i c duct = p ro xima l part of dor sa l pan cr ea t i c duct

Mc dev elopm en t a l an oma ly of p an crea s — Pan cr ea t i c divi sum

Ven t ra l m esog a st ri um Septum t ran sv er sum

1. Fa lci form l i g am en t
2. Cor onary l i g am en t
3. Trian gul ar l i g am en t

Sto ma ch 4. L^ esser^ om^ en^ tum^ H^ epa^ tog^ a^ st^ ri^ c^ l^ i^ g^ am^ en^ t H epa toduode na l l i g am en t

Dor sa l m esog a st ri um Spl an cn opleu ri c l a tera l pl a te m esode rm

1. Gr ea ter om en tum
2. Ga st rosple ni c l i g am en t
3. Splen or ena l l i g am en t
4. Ga t r oph r eni c l i g am en t

Midgut

6 th week Physi olog i ca l hernia t i on

Pre arteria l segm en t

Supe ri or m esen t ri c artery

Post arteria l seg m en t

U m bi l i ca l openin g

Hi ndgut & urogeni tal system

U r or ect a l septum

A ll an toi s

Clo a ca l m em bran e

Med ia l um bi l i ca l l i g am en t U^ ra^ chus

U r ogeni t a l sin us

U r ogeni t a l m em bran e

Primi t ive rectum

Ana l m em bran e E^ n^ dode^ rm

Den t a te l in e Ectode rm

In term edia te m esode rm

1. Geni t a l ri dge — Go na ds
2. Neph r ogeni c cor d

Mese n t ry

Yolk Sac

Prim ordia l ge rm cells

Mesonephric duct ( Wolffian duct )

M a le

1. Posteri or wa ll of p roxima l prost a t i c ur eth ra
2. U r et i c bud & i t’s de riva t iv es
3. Tri gon e
4. Sperma t i c pa thw a y

va s defe r en ce eja cul a tor y duct semina l vesi cle epi di dy mi s

5. A ppen dix of epi di dy mi s

Fema le

1. Poste ri or wa ll of ur eth ra
2. U r et i c bud & i t’s deriva t iv es
3. Tri gon e
4. Gar dn er’s duct ( duct of epoopho ron ) ( pr ese n t betwee n 2 l a yer s of Bro a d l i g am en t)

Para mesonephric duct

M a le

A ppen dix of T est i es Pr ost a t i c ut ri cles

Fema le

Fa llopian tube Uter us Uppe r part of va g ina